The invention relates to a shaft seal system and a compressor having a corresponding shaft seal system.
Seals are used to separate areas having a fluid from areas without such a fluid. Seals pressurized with gas have proven successful for such purpose (German Patent Document No. DE 1 106 567). The gas (for example, pressurized air) can be supplied using an independent compressor, as is described in the U.S. Pat. No. 4,350,345. This separate air compressor is unsuitable for transient gas turbines, since the former requires additional space and increases unnecessarily the weight of the gas turbine.
Instead, pressurized air is channeled off from the compressor. As long as the gas turbine is operated at sufficient capacity (for example, travel speed), the pressure difference at the seal pressurized with gas is sufficiently high, such that the fluid is unable to flow beyond this seal. As a result, the fluid remains in the desired area (for example, in a chamber).
If, on the other hand, the gas turbine is operated at idle, i.e., the gas turbine is operated at reduced capacity, the gas pressure generated by the compressor is then reduced and, therefore, also the pressure difference at the seal pressurized with gas. In such a case, the pressure difference may fall to the point that it is not sufficient to inhibit the fluid from passing the seal, such that the fluid is then able to flow past the seal. However, this has the disadvantage that other areas of the gas turbine may then become contaminated with this fluid (for example, lubricating oil). At worst, such contamination may result in a total breakdown of the gas turbine.
Thus, the object underlying the present invention is to provide a shaft seal system, which is independent of the capacity demanded of a gas turbine, without increasing the weight of the gas turbine in the process.
The invention relates to a shaft seal system, which is disposed axially between a first chamber and a second chamber. The shaft seal system includes a shaft, a casing that surrounds the shaft and at least one seal, which is disposed, in particular, axially closer to the second chamber, where the first chamber includes a fluid and the second chamber is to be protected from this fluid. The seal includes at least one mechanical pressure booster.
A fluid may be understood to mean a lubricating fluid and/or vapors of the lubricating fluid.
In one advantageous embodiment of the invention, the pressure booster is formed in such a way that the pressure of a sealing gas flowing at the seal and in the direction of the first chamber is increased. The pressure upstream from the first chamber advantageously builds up in such a way that no sealing fluid is able to escape from the first chamber into the second chamber.
In another advantageous embodiment of the invention, at least one pressure booster rotates during operation and/or at least one pressure booster is stationary, where the rotating pressure booster is preferably disposed at the axial height of the stationary pressure booster. Rotating in this case may be understood to mean that the pressure booster rotates synchronously with the shaft. Stationary may be understood to mean that the pressure booster is decoupled from the shaft rotation. Thus, for example, the casing or any component disposed on the casing is stationary.
In another advantageous embodiment of the invention, the pressure booster is a helical groove, disposed preferably on the inner circumference of the casing. It is also conceivable that, in addition or alternatively, the helical groove is disposed on or in the outer surface of the shaft. The helical groove may, for example, be an internal or external thread. The thread or the helical groove has a right rotation or a left rotation, depending on the direction of rotation of the shaft. The thread (or the helical groove) may have at least one complete winding. This advantageously forms an air vortex traveling around the shaft or on the casing and flowing in the direction of the first chamber.
In another advantageous embodiment of the invention, the pressure booster is an elevation and/or an indentation, which is preferably disposed on the shaft. It is also conceivable that, in addition or alternatively, the indentations and/or elevations may be disposed on, respectively, the casing. The indentations and/or elevations may, for example, be disposed directly on the casing or on the shaft, or an adapter piece is disposed on the casing (or shaft), on which indentations and/or elevations are disposed. Furthermore, the indentations and/or elevations may have a triangular cross-section. This has the advantage that the sealing air is increasingly carried in the circumferential direction. At least one elevation and/or at least one indentation may extend at an angle to the rotational axis of the shaft, as is also mentioned below.
An elevation in terms of the invention is additional material that protrudes above the outer surface of the shaft. On the other hand, an indentation in terms of the invention is removed material that has been extracted from the outer surface of the shaft, such that the indentation is integrated in the shaft. If the pressure difference produced at the seal is too small, the fluid is then able to flow out of the first chamber into the second chamber in an undesirable manner. The indentation in, or the elevations on, the shaft cause an additional build-up of gas pressure, so that the pressure difference is unable to drop below a critical value. This effectively prevents the fluid from flowing out of the first chamber into the second chamber. As a result, the elevations or indentations on or in the shaft divert an increased gas mass flow, preferably in the circumferential direction.
The elevations and/or the indentations may be disposed at the axial height of the helical groove, provided that the rotating pressure booster includes at least one elevation and/or one indentation and the stationary pressure booster includes at least one helical groove. This is understood to mean that the elevations and/or indentations, when viewed in the radial direction, are disposed exactly opposite the helical groove.
In one advantageous embodiment of the invention, at least one of the elevations and/or at least one of the indentations may extend at an angle to the rotational axis of the shaft. The angle to the rotational axis in such a case is selected so that the flow of the gas in the direction of the first chamber is increased, in order thereby to increase the gas pressure upstream from the first chamber.
In another advantageous embodiment of the invention, the shaft seal system includes at least one additional seal, which is disposed axially closer to the first chamber. Furthermore, the additional seal may be disposed radially between the shaft and the casing. The seal may be preferably spaced axially apart from the additional seal. In this way, the seal may be disposed upstream from the additional seal. The direction of flow, to which reference is made, points in the direction from the second chamber to the first chamber. The additional seal may be designed as a gas seal in the form of a labyrinth seal. In this way, the gas pressure (viewed in the flow direction) is preferably greater upstream from the additional seal than the gas pressure (viewed in the flow direction) downstream from the additional seal. The area downstream from the second seal may correspond to the area of the first chamber. It has proven advantageous to increase upstream from the additional seal the pressure of the sealing gas flowing at the seal and in the direction of the additional seal. This may ensure that even at low rotational speeds, the pressure from the additional seal is sufficiently high, such that harmful fluid from the first chamber is unable to flow at the additional seal in the direction of the seal.
In another advantageous embodiment of the invention, an annular space is present axially between the seal and the additional seal and radially between the shaft and the casing. Thus, the annular space, viewed in the flow direction, is disposed upstream from the additional seal and downstream from the seal. This annular space advantageously offers the possibility of temporarily storing the gas flowing in the direction of the first chamber, in order to be able to compensate for possible pressure fluctuations.
In another advantageous embodiment of the invention, a shoulder is disposed on the inside of the casing between the seal and the additional seal and radially between the shaft and the casing. The shoulder, projecting preferably radially inwardly, may have an internal radius that is smaller than the internal radius of the casing at the height of the seal, such that the internal radius of the internal thread is greater than the internal radius of the shoulder.
In another advantageous embodiment of the invention, the additional seal includes at least one sealing fin, in particular, on the outer surface of the shaft, and/or a lining, in particular on the inside of the casing. The sealing fin and the lining are preferably disposed at the same height in the axial direction, such that the sealing fin is able to cut into the lining. The lining may be an abradable lining or a honeycomb structure having abradable material.
In another advantageous embodiment of the invention, a sealing gas, preferably air, flows from the second chamber to the first chamber along the shaft. In this case, the sealing gas flows from the second chamber initially through the seal. The sealing gas, if present, then flows past the inwardly projecting shoulder into the annular space. Finally, the sealing gas flows through the additional seal into the first chamber.
In another advantageous embodiment of the invention, the sealing gas is supplied by a compressor, in particular, by an engine compressor. This has the advantage that no additional compressor is required in order, for example, to generate pressurized air.
Exemplary embodiments of the invention are described in greater detail below with reference to the schematic drawings.